_Origin._—From a broad area on the middle third of the upper side of the shaft of the ulna. _Insertion._—Near the top of the outer edge of the anchylosed os magnum of the carpo-metacarpus. _Shape._—Thin, somewhat flat. _Relations._—To the inside of the flexor digitorum profundus. _Action._—Flexes the hand upon the forearm and rotates the hand toward the body. OTHER MUSCLES OF THE DIGITS Extensor proprius pollicis Flexor minimi digiti Abductor minimi digiti Interosseous palmaris Flexor brevis pollicis Flexor minimi digiti brevis Interosseous dorsalis Flexor metacarpi brevis =Extensor Proprius Pollicis= (Fig. 13, No. 29a). _Location._—Anterior to the radio-carpal joint. _Origin._—From the ulnar side of the tendon of the extensor metacarpi radialis longior. _Insertion._—To the antero-ulnar side of the pollex. _Shape._—Small, spindle-shaped; tendinous at both attachments. _Relations._—Inferiorly, with the proximal and anterior part of the metacarpus. _Action._—An extensor of the pollex. =Flexor Brevis Pollicis= (Fig. 13, No. 28a). _Location._—Anterior to the pollex. _Origin._—From the shaft of the mid-metacarpal bone, just below the pollex. _Insertion._—Distal apex of the pollex. _Shape._—Short, small, fleshy. _Relations._—Superiorly, with the inferior part of the pollex. _Action._—Flexes the pollex. =Flexor Minimi Digiti.= _Location._—Inferior side of the metacarpus. _Origin._—From the posterior part of the median metacarpal close to the os carpi ulnare. A few fibers extend to the ulna. _Insertion._—Into the base of the median phalanx. _Shape._—Small, slender, short. _Relations._—Superiorly, with the metacarpal bone. _Action._—A flexor of the digit. =Flexor Minimi Digiti Brevis= (Fig. 13, No. 30). _Location._—Inferior to the third, or small finger. _Origin._—From the lower and posterior end of the median metacarpal and from the adjacent tendon of the preceding. _Insertion._—Inserted to the apex of the small finger. _Shape._—Small and rather rudimentary. _Relations._—Inferior to the small finger. _Action._—Acts as a posterior ligament of this joint. =Abductor Minimi Digiti.= _Location._—Supero-lateral side of the small finger. _Origin._—From the proximal extremity of the anterior aspect of the third finger. _Insertion._—To the posterior border of the proximal phalanx of the second, or index-finger at a point just above the tip of the third finger. _Shape._—A few muscular fibers with some tendinous material. _Relations._—At the base of the median segment of the index-finger and to the side of the third. _Action._—Antagonizes the powerful flexors on the back of the joint. =Interosseus Dorsalis= (Fig. 13, No. 31). _Location._—By the side of the metacarpus.